1. Field of the Invention
The present invention relates to an automatic document feeder and, more particularly, to an automatic document feeder used in an image forming apparatus.
2. Description of the Related Art
A typical automatic document feeder (ADF) that is used in an image forming apparatus, such as a facsimile machine, a copying machine, and a multifunction product (MFP), includes a paper feed tray on which a plurality of originals can be placed. A set of originals is picked up one by one from the paper feed tray, conveyed to an image scanning position, and then discharged to a discharge tray.
The typical ADF detects a jam that occurs on a conveying path between the paper feed tray and the discharge tray to protect the original.
To determine a jam, the typical ADF calculates an original length from an original size received via a control panel (hereinafter, “input original length”) and sets the input original length as a jam determining value. The ADF calculates an original length using original detection sensors arranged on the conveying path (hereinafter, “actual original length”), and determines whether a jam occurs by comparing the actual original length with the jam determining value (see, for example, Japanese Patent Application Laid-open No. 2003-54786).
The ADF disclosed in the Japanese Patent Application Laid-open No. 2003-54786 compares the input original length received via the control panel of a main body of the image forming apparatus with an original length that is calculated based on a detection result from original length sensors arranged on a paper feed tray (hereinafter, “detected original length”), and sets a larger value between the input original length and the detected original length as the jam determining value. While the original is conveyed, the ADF measures a conveying amount of the original based on a detection result obtained from a registration sensor and a discharging sensor, thereby calculating the actual original length. When the actual original length is larger than the jam determining value, the ADF determines that the original has jammed. The ADF performs jam detection control by notifying the main body of the image forming apparatus of the jam and stopping motors, solenoids, or the like.
With this configuration, images are properly scanned even when a user fails to input a correct original size, in particular, when the user inputs a smaller value than the actual original length.
A way to determine timing to feed a next page of the originals (hereinafter, “subsequent-original feeding timing”) based on the detected original length calculated according to information from the sensor arranged on the paper feed tray is known.
However, the ADF disclosed in the Japanese Patent Application Laid-open No. 2003-54786 requires a plurality of sensors for detecting the original size to be arranged on the paper feed tray. This disadvantageously makes the configuration of the ADF complicated and increases the cost of the ADF.
When detecting the maximum conveyable non-standard-size original, because an original length sensor for calculating the original length of this size has to be arranged, thus requiring the paper feed tray corresponding to the maximum conveyable original size. Accordingly, the size of the ADF becomes large.
Furthermore, other than the jam determining value, with the known ADF in which the subsequent-original feeding timing is determined based on the original length that is calculated based on the information from the sensor arranged on the paper feed tray, there is also a similar problem.